High-current seal for electric discharge lamp



T. c. RETZER 3,

HIGH-CURRENT SEAL FOR ELECTRIC DISCHARGE LAMP Oct. 11, 1966 Filed April 26. 1965 FIG. 2.

INVENTOR. THEODORE C. RETZER.

United States Patent 3,278,778 HIGH-CURRENT SEAL FOR ELECTRIC DISQHARGE LAMP Theodore C. Retzer, Cedar Grove, N1, assiguor to Westinghonse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 26, 1963, Ser. No. 275,939 Claims. (Cl. 313-43) This invention relates to seals and has particular reference to ribbon seals for short-arc'mercury or xenon electric discharge lamps of high wattage rating.

One of the most expensive and critical items in a short are electric discharge lamp are the seals. This is primarily due to the fact that they must not only meet the stringent current-carrying requirements of such lamps but must do so without rupturing or otherwise exposing the lead-in conductors to excessive oxidation despite the extremely high operating temperatures that prevail during use. In one type of seal designed for short-arc lamps having a rating of about 500 watts or so, several met-a1 ribbons are mounted on a vitreous core to form a lead-in conductor assembly which is subsequently sealed into a tubular arm that is attached to the envelope. The outer ends of the ribbons are connected to a conductor rod and the envelope arm is provided with a graded seal at its outer end so that it can be sealed directly to the rod. A seal of this character and the method of making it are described in U.S. Patent No. 2,682,009 issued June 22, 1954, to H. D. Fraser.

While the aforementioned seal construction is satisfactory for lamps of relatively .low wattage (below 1 k.w.), it is much too expensive for use in lamps having ratings of 5 kW. and above because of the large diameter electrodes required. Since the electrodes are inserted into the envelope through the arms during assembly, the diameter and cost of the graded seals increase markedly as the size of the electrodes increase.

It is accordingly the general object of the present invention to provide an improved seal for short-arc lamps of high-wattage rating.

Another object is the provision of a high-current seal for multi-kilowatt short-arc lamps that is inexpensive, rugged and easy to make.

Still another object is the provision of a seal assembly that will permit short-arc lamps having large diameter electrodes to be fabricated using graded seals of conventional size.

The aforesaid objects, and other advantages which will become apparent as the description proceeds, are achieved in accordance with the present invention by joining the outer end of the envelope arm to the lead-in conductor rod by means of a re-entrant stem which includes the graded seal component. This construction avoids the expense and complications encountered when the graded seal is made part of the envelope arm and then sealed directly to the conductor rod as in the prior art practice. As a result, graded seals of standard size may be used even though the diameter of the electrode and, hence of the envelope arms, are quite large.

In addition, since the end of the envelope arm need only be sealed to the flared end of the stern assembly instead of directly to the much smaller lead-in conductor rod, the sealing-in operation and fabrication of the lamp are greatly facilitated.

A better understanding of the invention will be obtained by referring to the accompanying drawing, wherein:

FIGURE 1 is an elevational view, partly in section, of a 5 kw. short-arc lamp incorporating the improved seal of the present invention;

Patented Oct. 11, 1966 'ice FIG. 2 is an enlarged fragmentary view, mainly in section, of the electrode and lead-in conductor assembly before it is inserted into the envelope arm and sealed therein;

FIG. 3 is a cross-sectional view through the seal of the completed lamp along the line IIIIH of FIG. 1;

FIG. 4 is an elevational view, partly in section, illustrating the first step in fabricating the seal in accordance with the invention; and,

FIG. 5 is a cross-sectional view through the partlyfabricated seal along the line VV of FIG. 4 and illustrates the spacing that is initially present between the seal assembly and the envelope arm.

While the improved seal of the present invention can be advantageously used in various types of electrical devices, it is especially adapted for use in conjunction with short-arc lamps that require massive electrodes and it has accordingly been so illustrated and will be so described.

Construction In FIG. 1 there is shown a 5 kw. mercury short-arc lamp 10 comprising an envelope 12 of quartz or similar high-temperature vitreous material having a pair of oppositely disposed arms 14 and 15 through which the leadin conductor assemblies are sealed. This particular lamp is designed for DC. operation and accordingly contains a cathode 16 and a relatively massive anode 18 which project into the bulbous portion of the envelope from the aforesaid arms. The envelope contains a charge of mercury and an inert starting gas such as argon. If desired, a filling of Xenon gas at a pressure of about 1 to 5 atmospheres can be used, with or without the mercury. Evacuation of the envelope 12 before the introduction of the ionizable medium is accomplished through an exhaust tubulation which is subsequently sealed off in the usual manner to leave a short tip 13.

The cathode 16 and anode 18 are each held in opposing relationship within the envelope 12 by a support rod 20 that is anchored in the sealed portion of the respective arms. Since each of the seals are identical, only the one formed with the upwardly extending arm of the lamp as viewed in FIG. 1 will be described. As shown, one end of the support rod 20 is anchored in a vitreous core 22 that is preferably fabricated from quartz and is fused with the encircling end portion of the arm 14. A lead-in conductor rod 24 is anchored in the opposite end of the core 22 and extends through the arm 14 to the end thereof where it is joined to a flexible lead 32 by means of a nickel sleeve 33. The support rod 20 and conductor rod 24 are electrically connected by a series of thin metal ribbons 21 that are hermetically embedded in the sealed off portion of the arm 14 and joined to the ends of the foregoing rods.

The simplification and reduction in the cost of the seal is achieved in accordance with the present invention by anchoring the outer end of the lead-in conductor rod 24 within the arm 14 by means of a re-entrant stem 28 that is sealed to the end of the arm and hermetically fused around an intermediate portion of the conductor rod. As shown in FIG. 1, this stern consists of a glass bushing 29 that is joined to a tubular graded seal 30 which, in turn, is joined to a quartz flare 31.

As shown in FIG. 2, the cathode 16, its support rod 20, the quartz core 22, conductor rod 24, stem 28, and the ribbon conductors 21 are joined together in the abovedescribed manner to form a seal assembly 36 that is insertable into the tubular arm 14 of the envelope 12. In this particular embodiment, four ribbon conductors 21 of molybdenum or the like are employed and uniformly spaced around the periphery of and extend along the core 22, which is of cylindrical configuration see FIGS. 1 and 5). The core thus serves as a supporting mandrel for the delicate ribbons. The ends of the main ribbons 21 are spot welded to heavier jumper ribbons 23 the ends of which are fastened to the conductor rod by several turns of platinizedmolybdenum ribbon 25. The opposite ends of the ribbon conductors 21 are similarly fastened to the support rod 20 by jumper ribbons 23 and several turns of ribbons 25. As will be noted, the glass bushing 29 which comprises the inner end of the stem 28 is sealed to an intermediate portion of the conductor rod 24 and the latter extends through the stem 28 to the end of the flared portion 31 thereof.

The tubular graded seal 30 constitutes the intermediate portion of the stem 28 and consists of a series of glass rings that are joined together and have slightly different and progressively higher expansion coetficients. The glass at the end of the graded seal 30 joined to the quartz flare 31 has a low coeificient of expansion whereas the one at the opposite end that is joined to the glass bushing 29 has a much higher coefficient. The stem 28, accordingly, compensates for the marked difference in the coeificients of expansion of the metal conductor rod 24 and the quartz arm of the envelope 12 and permits one end of the stem to be sealed directly around the rod and the other end of the stem to be sealed directly to the envelope arm without the danger of thermally induced strains and cracks. Since the stem 28 is located within the outer end portion of the arm 14, graded seals 30 of conventional size can be used even though the size of the lamp is such that it requires massive electrodes and large diameter arms.

The bushing29 is made from a glass such as uranium glass (Corning 3320) that has a high coefiicient of expansion and can be sealed directly to tungsten.

' In order to protect the ends of the jumper ribbons 23' and the ribbon wrapping 25' located adjacent the cathode 16 a collar 34 of quartz is preferably placed over this portion of the seal assembly 36, as shown in FIG. 2, and is so dimensioned that it is held in this position by means of a force fit with the wrapping 25.

As a specific example of the dimensions of the various parts, in the case of the 5 kw. short-arc lamp here shown having tubular arms about 1 /8 in diameter, the diameter of the stem 28 was about /8" and increased to a dimension of about 1 /8" at its flared end. The diameter of the quartz core 22 and protective collar 34 were approximately the same as that of the stem. The lead-in conductor rod 24 was fabricated from tungsten and its outer end about 0.150" in diameter and its enlarged inner end was about A" in diameter. The support rod 20 was also fabricated from tungsten and was of substantially the same size as the enlarged end of the conductor rod. The conductor ribbons 21 were made of molybdenum and were 0.0012" thick and wide. The jumper ribbons 23 were 0.004 thick and 0.125" wide. The jumper ribbons were also fabricated from molybdenum. The wrappings 25 and 25' consisted of platinized molybdenum ribbon 1 mm. wide x 0.003 thick.

Fabrication In fabricating the improved seal, the seal assembly 36 attached to the cathode 16 is first inserted into the arm 14 of the quartz envelope 12 until the flared end of the stem 28 abuts against the end of the arm. The assembly attached to the anode 18 is then similarly inserted into the other arm 15. The partially assembled lamp is then placed in a chuck which grips the respective arms at points overlying the stems and the entire assembly is rotated through a pair of sealing fires 37 and 38 (see FIG. 4) that seals the flared ends of the stems to the ends of the respective arms. This anchors the electrodes in aligned prede termined position with respect to each other and seals off the arms from the atmosphere. The envelope 12 is then evacuated through the exhaust tube which is then tippedoff at a point remote from the envelope.

The partially assembled lamp is again rotated and the sealing fires are positioned to impinge on the portion of the arm 14 that encircles the outer end of the core 22. The resultant softening of the arm causes it to sink down onto the core and interposed ribbon conductors 21 thus fusing the quartz members together and hermetically embedding the ribbons in the resulting solid body of quartz. The fires are then slowly advanced until the remaining portion of the arm that encircles the core and the protective collar 34 is heated and collapsed, the rotation of the lamp being maintained to effect uniform heating. Thus, the portion of the arm 14 extending from approximately its midpoint to a point just short of the bulbous body portion of the envelope 12 is sealed off and hermetically united with the core 22. The outermost end portion of the arm, however, retains its original form and defines, in conjunction with the sealed-in stem 28, an evacuated chamber A, as shown in FIG. 1. The chamber A is thus substantially devoid of oxygen and serves as a protective enclosure for an intermediate portion of the conductor rod 24.

The other arm 15 of the envelope is processed in the same manner thus completing the assembly of the lamp.

The ribbon conductors 21 are, accordingly, hermetically embedded within the sealed portions of the arms, as shown in FIG. 3, and provide a seal capable of carrying the high current required to operate the lamp. By properly selecting the size of the various parts seals capable of handling currents of or 200 amperes and higher can be readily made, in accordance with this method of manufacture using graded seals of standard size.

It will be appreciated from the foregoing that the objects of the invention have been achieved insofar as an improved seal for high-wattage short-arc lamps has been provided which can be conveniently fabricated and tailored to accommodates electrodes of various sizes without increasing the cost of the lamp.

While a preferred embodiment has been described in detail, it will be appreciated that various changes in both the configuration and arrangement of parts and manner of assembly can be made without departing from the spirit and scope of this invention.

I claim as my invention:

1. A seal for a short-arc electric discharge lamp or the like having a vitreous envelope comprising, in combination;

a vitreous arm attached to and extending from said envelope,

at vitreous core fused with and hermetically closing the end of said arm that is joined to said envelope,

an elongated electrode having one end anchored in said core and its opposite end disposed in said envelope,

a rigid lead-in conductor anchored in the other end of said core and extending outwardly toward the end of said arm,

a ribbon conductor hermetically embedded in the sealed portion of said arm and electrically connecting said lead-in conductor to said electrode, and

a re-entrant vitreous stem that includes a graded seal component,

said stern being located within the outer end portion of said arm and having its outwardly-disposed end hermetically sealed to the proximate end of said arm and its other end hermetically sealed around an intermediate portion of said rigid lead-in conductor so that said stem, in conjunction with the sealed-in vitreous core, provides a chamber within said arm that (a) is sealed-off from the discharge space defined by the envelope and (b) protectively encloses an intermediate portion of said lead-in conductor.

2. A seal as set forth in claim 1 wherein said chamber is substantially free of oxygen.

3. A seal as set forth in claim 1 wherein the outwardlydisposed end of said stem that is sealed to said arm is flared and protrudes laterally beyond the body of the stem, and said chamber is evacuated.

4. An assembly adapted for use in an hermetic seal structure for a short-arc electric discharge lamp having a vitreous envelope with an outwardly extending arm, said assembly comprising;

an elongated core of vitreous material,

a metal rod anchored in and extending longitudinally from one end of said core,

an electrode attached to the free end of said rod,

a rigid lead-in conductor anchored in and extending longitudinally from the other end of said vitreous core,

a plurality of spaced metal ribbon conductors on and extending along said vitreous core,

means electrically connecting the ends of said ribbon conductors with the proximate ends of said metal rod and rigid lead-in conductor, and

a tubular stem comprising (a) a vitreous bushing, (b) a graded steel component and (c) a vitreous flare joined end-to-end in the aforesaid order with the protruding portion of said flare disposed at one end of said stem,

said vitreous bushing being hermetically sealed around i the flared segment of said stem has a lower coefficient of expansion than the vitreous bushing, and

the flared end of said stem and the end of the envelope Y I arm have substantially the same cross-sectional configuration and dimensions.

References Cited by the Examiner UNITED STATES PATENTS 2,982,877 5/1961 Heine-Geldern 3l3184 3,140,417 7/1964 Tietze 3l3--266 X 3,154,713 10/1964 Beese 313267 JOHN'W. HUCKERT, Primary Examiner.

R. F. POLISSACK, Assistant Examiner. 

1. A SEAL FOR A SHORT-ARC ELECTRIC DISCHARGE LAMP OR THE LIKE HAVING A VITREOUS ENVELOPE COMPRISING, IN COMBINATION; A VITREOUS ARM ATTACHED TO AND EXTENDING FROM SAID ENVELOPE, A VITREOUS CORE FUSED WITH AND HERMETICALLY CLOSING THE END OF SAID ARM THAT IS JOINED TO SAID ENVELOPE, AN ELONGATED ELECTRODE HAVING ONE END ANCHORED IN SAID CORE AND ITS OPPOSITE END DISPOSED IN SAID ENVELOPE, A RIGID LEAD-IN CONDUCTOR ANCHORED IN THE OTHER END OF SAID CORE AND EXTENDING OUTWARDLY TOWARD THE END OF SAID ARM, A RIBBON CONDUCTOR HERMETICALLY EMBEDDED IN THE SEALED PORTION OF SAID ARM AND ELECTRICALLY CONNECTING SAID LEAD-IN CONDUCTOR TO SAID ELECTRODE, AND A RE-ENTRANT VITREOUS STEM THAT INCLUDES A GRADED SEAL COMPONENT, SAID STEM BEING LOCATED WITHIN THE OUTER END PORTION OF SAID ARM AND HAVING ITS OUTWARDLY-DISPOSED END HERMETICALLY SEALED TO THE PROXIMATE END OF SAID ARM AND ITS OTHER END HERMETICALLY SEALED AROUND AN INTERMEDIATE PORTION OF SAID RIGID LEAD-IN CONDUCTOR SO THAT SAID STEM, IN CONJUNCTION WITH THE SEALED-IN VITREOUS CORE, PROVIDES A CHAMBER WITHIN SAID ARM THAT (A) IS SEALED-OFF FROM THE DISCHARGE SPACE DEFINED BY THE ENVELOPE AND (B) PROTECTIVELY ENCLOSES AN INTERMEDIATE PORTION OF SAID LEAD-IN CONDUCTOR. 